In the 50-s, prof. K.V. Ruppeneit investigated the mechanism of transfer of rock pressure forces between neighboring individual blocks in a fractured rock mass. Experiments were performed to fill the cracks between the blocks of the array with liquid wax or liquid lead. After cooling of the wax or lead, the rock mass was carefully disassembled in order to extract a “cast” of rock contacts. As a result of many experiments, K.V. Ruppeneit found that the area of directly rocky contacts, namely, the holes in the "casts" - is only 3-4% of the surface of the entire crack between the blocks in the massif. The transfer of pressure forces is carried out through the point contact of the blocks, and basically, the surface of the crack is free from the transfer of pressure forces between the blocks. To determine the necessary stability of the exhaust workings, an assessment was made of the influence of the weight of a column of broken rock mass on their wear. At the same time, the conditions of the necessary strength and stability of the base of the blocks destroyed by the pressure of the weight of the column of the broken rock mass were determined. There are several options for the construction of the base of the blocks: for the release and delivery of PDM ore, trenches and funnels for VDPU and scraper delivery. When ore is released, the contacts of moving pieces of rock with the surface of the funnel are formed only on the surfaces of their contact. The load due to the weight of the column of broken rock does not act on the entire surface of the funnel, but only on the contact points of the pieces of ore with its surface. Therefore, on the basis of physical modeling, the area of rock contacts of pieces of broken rock mass with the surface of the funnel was determined; this ensured a geometric, dynamic and functional similarity to the model in nature, in which the dimensions of the funnels and the fractional composition were observed. With dynamic similarity, the bulk density of ore represented by quartzites and magnetites was observed. In functional modeling, the weight of a column of broken ore with a height of 100 m was observed. Studies were conducted on models made at a scale of 1:50 from full-scale. The area of rock contacts was determined by scanning on the computer the surface of an expanded truncated cone - an expanded funnel of release with dark spots of rock contacts, with a different ratio of fractions in the broken rock mass. Further, using a computer, their absolute and relative area was de-termined. Since the base of the block is an array cut by outlet funnels having inclined lateral surfaces to the horizon, as is known, there is also a force acting on the shearing (shear) of rocks by the weight of a column of broken rock mass. It was necessary to determine which of the above forces exerts the greatest destructive effect on the base of the block during the mining of rock mass, and based on this information, determine the permissible height of the beaten out ore layer during mining of the ore deposit. Calculations were made of the solid base of the block under the action of crushing and shearing forces, from which it was revealed that when pieces of broken ore act on the inclined surface of the outlet funnel, the destruction of the surface of the funnel occurs primarily due to the shearing component of the column weight forces of the broken rock mass. Calculations show that the column of rock mass creates a shearing force, 2.1 times higher than when crushed. Further, similarly, the calculations of the effect of crushing and shearing forces on the weight of a column of broken rock mass for various sizes of funnels were made. Based on the calculations, the dependence of the permissible maximum output volume of the rock mass on the value of the coefficient of rock contacts was established. For mining systems with caving of ore and host rocks Acad. Malakhov G.M. it was determined that the ratio of the total height of the column of ore and overlying rocks to the height of the collapsed ore mass should in the optimal case be 2.7–3.5, depending on the fractional composition and strength of the ore. Therefore, for these systems, knowing the total height of the broken rock mass, it is possible to determine the optimal allowable height of the beaten ore layer in the floor. Computer analysis of the various variants of the fractional composition was carried out with a change in the specific gravity of each fraction. Each of the considered fractional compositions is most characteristic of the mines of GornayaShoria, Abakan RU, JSC «PIMCU», Krivbas, copper mines of Chile, Australia, and India. The largest value of the rocky contacts will correspond to the granular composition, in which the ore is represented only by small fractions. In reality, it is impossible to achieve this during blasting, therefore the recommendations come to the following: based on the calculations, the most rational fractional composition of the ore to be mined is established with a known shear strength and the corresponding height of the ore bed to be mined, which is recommended for the preparation of a blasting certificate. The results obtained during the design of mining operations determine the optimal height of the striking layer in systems with mass collapse, as well as in chamber systems, during the development of powerful ore deposits, and prevent the risk of premature wear of the foundations of blocks during the release of broken rock mass.
|Issue||2019, № 4 (Т. 11)|
|Key words||outlet funnels, physical model, rock contacts, forces, computer programs, column of broken ore, fractional composition, nomogram.|